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repl: Assignment of _ allowed with warning by lance · Pull Request #5535 · nodejs/node

@mscdex added the repl

Issues and PRs related to the REPL subsystem.

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Mar 2, 2016

@jasnell jasnell added the semver-major

PRs that contain breaking changes and should be released in the next major version.

label

Mar 3, 2016 
This commit addresses #5431 by
changing the way that the repl handles assignment to the global _
variable.

Prior to this commit, node sets the result of the last expression
evaluated in the repl to `_`. This causes problems for users of
underscore, lodash and other packages where it is common to assign
`_` to the package, e.g. `_ = require('lodash');`.

Changes in this commit now result in the following behavior.

- If unassigned on the repl, `_` continues to refer to the last
  evaluated expression.
- If assigned, the default behavior of assigning `_` to the last
  evaluated expression is disabled, and `_` now references whatever
  value was explicitly set. A warning is issued on the repl -
  'expression assignment to _ now disabled'.
- If `_` is assigned multiple times, the warning is only displayed once.
- When `.clear` is executed in the repl, `_` continues to refer to its
  most recent value, whatever that is (this is per existing behavior).
  If `_` had been explicitly set prior to `.clear` it will not change
  again with the evaluation of the next expression.
Ensures that, when invoking `.clear` in a repl, the underscore
assignment behavior is reset, so that its value is again set to the most
recently evaluated expression.

Additional tests have been added for the behavior of `let` when underscore
assignment has been disabled.
Adds a line of text about the behavior of `_` in the REPL.

@lance 

Add a test based on feedback from @cjihrig. Ensures that when used
in 'magic' mode, the behavior of `_` assignment is consistent with
other modes and user expectations.
When a REPL user explicitly assigns `_` the warning text now reads,
"Expression assignment to _ now disabled.".

Also removed an unnecessary parameter from a test helper function.

silverwind pushed a commit that referenced this pull request

Mar 18, 2016 
This commit addresses #5431 by
changing the way that the repl handles assignment to the global _
variable.

Prior to this commit, node sets the result of the last expression
evaluated in the repl to `_`. This causes problems for users of
underscore, lodash and other packages where it is common to assign
`_` to the package, e.g. `_ = require('lodash');`.

Changes in this commit now result in the following behavior.

- If unassigned on the repl, `_` continues to refer to the last
  evaluated expression.
- If assigned, the default behavior of assigning `_` to the last
  evaluated expression is disabled, and `_` now references whatever
  value was explicitly set. A warning is issued on the repl -
  'expression assignment to _ now disabled'.
- If `_` is assigned multiple times, the warning is only displayed once.
- When `.clear` is executed in the repl, `_` continues to refer to its
  most recent value, whatever that is (this is per existing behavior).
  If `_` had been explicitly set prior to `.clear` it will not change
  again with the evaluation of the next expression.

PR-URL: #5535
Fixes: #5431
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>

jasnell added a commit that referenced this pull request

Apr 26, 2016 
The following significant (semver-major) changes have been made since the
previous Node v5.0.0 release.

* Buffer
  * New Buffer constructors have been added
    [#4682](#4682)
  * Previously deprecated Buffer APIs are removed
    [#5048](#5048),
    [#4594](#4594)
  * Improved error handling [#4514](#4514)
* Cluster
  * Worker emitted as first argument in 'message' event
    [#5361](#5361).
* Crypto
  * Improved error handling [#3100](#3100),
    [#5611](#5611)
  * Simplified Certificate class bindings
    [#5382](#5382)
  * Improved control over FIPS mode
    [#5181](#5181)
  * pbkdf2 digest overloading is deprecated
    [#4047](#4047)
* Dependencies
  * Reintroduce shared c-ares build support
    [#5775](#5775).
  * V8 updated to 5.0.71.31 [#6111](#6111).
* DNS
  * Add resolvePtr API to query plain DNS PTR records
    [#4921](#4921).
* Domains
  * Clear stack when no error handler
  [#4659](#4659).
* File System
  * The `fs.realpath()` and `fs.realpathSync()` methods have been updated
    to use a more efficient libuv implementation. This change includes the
    removal of the `cache` argument and the method can throw new errors
    [#3594](#3594)
  * FS apis can now accept and return paths as Buffers
    [#5616](#5616).
  * Error handling and type checking improvements
    [#5616](#5616),
    [#5590](#5590),
    [#4518](#4518),
    [#3917](#3917).
  * fs.read's string interface is deprecated
    [#4525](#4525)
* HTTP
  * 'clientError' can now be used to return custom errors from an
    HTTP server [#4557](#4557).
* Modules
  * Current directory is now prioritized for local lookups
    [#5689](#5689)
  * Symbolic links are preserved when requiring modules
    [#5950](#5950)
* Net
  * DNS hints no longer implicitly set
    [#6021](#6021).
  * Improved error handling and type checking
    [#5981](#5981),
    [#5733](#5733),
    [#2904](#2904)
* Path
  * Improved type checking [#5348](#5348).
* Process
  * Introduce process warnings API
    [#4782](#4782).
  * Throw exception when non-function passed to nextTick
    [#3860](#3860).
* Readline
  * Emit key info unconditionally
    [#6024](#6024)
* REPL
  * Assignment to `_` will emit a warning.
    [#5535](#5535)
* Timers
  * Fail early when callback is not a function
    [#4362](#4362)
* TLS
  * Rename 'clientError' to 'tlsClientError'
    [#4557](#4557)
  * SHA1 used for sessionIdContext
    [#3866](#3866)
* TTY
  * Previously deprecated setRawMode wrapper is removed
    [#2528](#2528).
* Util
  * Changes to Error object formatting
    [#4582](#4582).
* Windows
  * Windows XP and Vista are no longer supported
    [#5167](#5167),
    [#5167](#5167).

jasnell added a commit that referenced this pull request

Apr 26, 2016 
The following significant (semver-major) changes have been made since the
previous Node v5.0.0 release.

* Buffer
  * New Buffer constructors have been added
    [#4682](#4682)
  * Previously deprecated Buffer APIs are removed
    [#5048](#5048),
    [#4594](#4594)
  * Improved error handling [#4514](#4514)
* Cluster
  * Worker emitted as first argument in 'message' event
    [#5361](#5361).
* Crypto
  * Improved error handling [#3100](#3100),
    [#5611](#5611)
  * Simplified Certificate class bindings
    [#5382](#5382)
  * Improved control over FIPS mode
    [#5181](#5181)
  * pbkdf2 digest overloading is deprecated
    [#4047](#4047)
* Dependencies
  * Reintroduce shared c-ares build support
    [#5775](#5775).
  * V8 updated to 5.0.71.31 [#6111](#6111).
* DNS
  * Add resolvePtr API to query plain DNS PTR records
    [#4921](#4921).
* Domains
  * Clear stack when no error handler
  [#4659](#4659).
* File System
  * The `fs.realpath()` and `fs.realpathSync()` methods have been updated
    to use a more efficient libuv implementation. This change includes the
    removal of the `cache` argument and the method can throw new errors
    [#3594](#3594)
  * FS apis can now accept and return paths as Buffers
    [#5616](#5616).
  * Error handling and type checking improvements
    [#5616](#5616),
    [#5590](#5590),
    [#4518](#4518),
    [#3917](#3917).
  * fs.read's string interface is deprecated
    [#4525](#4525)
* HTTP
  * 'clientError' can now be used to return custom errors from an
    HTTP server [#4557](#4557).
* Modules
  * Current directory is now prioritized for local lookups
    [#5689](#5689)
  * Symbolic links are preserved when requiring modules
    [#5950](#5950)
* Net
  * DNS hints no longer implicitly set
    [#6021](#6021).
  * Improved error handling and type checking
    [#5981](#5981),
    [#5733](#5733),
    [#2904](#2904)
* Path
  * Improved type checking [#5348](#5348).
* Process
  * Introduce process warnings API
    [#4782](#4782).
  * Throw exception when non-function passed to nextTick
    [#3860](#3860).
* Readline
  * Emit key info unconditionally
    [#6024](#6024)
* REPL
  * Assignment to `_` will emit a warning.
    [#5535](#5535)
* Timers
  * Fail early when callback is not a function
    [#4362](#4362)
* TLS
  * Rename 'clientError' to 'tlsClientError'
    [#4557](#4557)
  * SHA1 used for sessionIdContext
    [#3866](#3866)
* TTY
  * Previously deprecated setRawMode wrapper is removed
    [#2528](#2528).
* Util
  * Changes to Error object formatting
    [#4582](#4582).
* Windows
  * Windows XP and Vista are no longer supported
    [#5167](#5167),
    [#5167](#5167).

jasnell added a commit that referenced this pull request

Apr 26, 2016 
The following significant (semver-major) changes have been made since the
previous Node v5.0.0 release.

* Buffer
  * New Buffer constructors have been added
    [#4682](#4682)
  * Previously deprecated Buffer APIs are removed
    [#5048](#5048),
    [#4594](#4594)
  * Improved error handling [#4514](#4514)
* Cluster
  * Worker emitted as first argument in 'message' event
    [#5361](#5361).
* Crypto
  * Improved error handling [#3100](#3100),
    [#5611](#5611)
  * Simplified Certificate class bindings
    [#5382](#5382)
  * Improved control over FIPS mode
    [#5181](#5181)
  * pbkdf2 digest overloading is deprecated
    [#4047](#4047)
* Dependencies
  * Reintroduce shared c-ares build support
    [#5775](#5775).
  * V8 updated to 5.0.71.31 [#6111](#6111).
* DNS
  * Add resolvePtr API to query plain DNS PTR records
    [#4921](#4921).
* Domains
  * Clear stack when no error handler
  [#4659](#4659).
* File System
  * The `fs.realpath()` and `fs.realpathSync()` methods have been updated
    to use a more efficient libuv implementation. This change includes the
    removal of the `cache` argument and the method can throw new errors
    [#3594](#3594)
  * FS apis can now accept and return paths as Buffers
    [#5616](#5616).
  * Error handling and type checking improvements
    [#5616](#5616),
    [#5590](#5590),
    [#4518](#4518),
    [#3917](#3917).
  * fs.read's string interface is deprecated
    [#4525](#4525)
* HTTP
  * 'clientError' can now be used to return custom errors from an
    HTTP server [#4557](#4557).
* Modules
  * Current directory is now prioritized for local lookups
    [#5689](#5689)
  * Symbolic links are preserved when requiring modules
    [#5950](#5950)
* Net
  * DNS hints no longer implicitly set
    [#6021](#6021).
  * Improved error handling and type checking
    [#5981](#5981),
    [#5733](#5733),
    [#2904](#2904)
* OS X
  * MACOSX_DEPLOYMENT_TARGET has been bumped up to 10.7
    [#6402](#6402).
* Path
  * Improved type checking [#5348](#5348).
* Process
  * Introduce process warnings API
    [#4782](#4782).
  * Throw exception when non-function passed to nextTick
    [#3860](#3860).
* Readline
  * Emit key info unconditionally
    [#6024](#6024)
* REPL
  * Assignment to `_` will emit a warning.
    [#5535](#5535)
* Timers
  * Fail early when callback is not a function
    [#4362](#4362)
* TLS
  * Rename 'clientError' to 'tlsClientError'
    [#4557](#4557)
  * SHA1 used for sessionIdContext
    [#3866](#3866)
* TTY
  * Previously deprecated setRawMode wrapper is removed
    [#2528](#2528).
* Util
  * Changes to Error object formatting
    [#4582](#4582).
* Windows
  * Windows XP and Vista are no longer supported
    [#5167](#5167),
    [#5167](#5167).

jasnell added a commit that referenced this pull request

Apr 26, 2016 
The following significant (semver-major) changes have been made since the
previous Node v5.0.0 release.

* Buffer
  * New Buffer constructors have been added
    [#4682](#4682)
  * Previously deprecated Buffer APIs are removed
    [#5048](#5048),
    [#4594](#4594)
  * Improved error handling [#4514](#4514)
* Cluster
  * Worker emitted as first argument in 'message' event
    [#5361](#5361).
* Crypto
  * Improved error handling [#3100](#3100),
    [#5611](#5611)
  * Simplified Certificate class bindings
    [#5382](#5382)
  * Improved control over FIPS mode
    [#5181](#5181)
  * pbkdf2 digest overloading is deprecated
    [#4047](#4047)
* Dependencies
  * Reintroduce shared c-ares build support
    [#5775](#5775).
  * V8 updated to 5.0.71.31 [#6111](#6111).
* DNS
  * Add resolvePtr API to query plain DNS PTR records
    [#4921](#4921).
* Domains
  * Clear stack when no error handler
  [#4659](#4659).
* File System
  * The `fs.realpath()` and `fs.realpathSync()` methods have been updated
    to use a more efficient libuv implementation. This change includes the
    removal of the `cache` argument and the method can throw new errors
    [#3594](#3594)
  * FS apis can now accept and return paths as Buffers
    [#5616](#5616).
  * Error handling and type checking improvements
    [#5616](#5616),
    [#5590](#5590),
    [#4518](#4518),
    [#3917](#3917).
  * fs.read's string interface is deprecated
    [#4525](#4525)
* HTTP
  * 'clientError' can now be used to return custom errors from an
    HTTP server [#4557](#4557).
* Modules
  * Current directory is now prioritized for local lookups
    [#5689](#5689)
  * Symbolic links are preserved when requiring modules
    [#5950](#5950)
* Net
  * DNS hints no longer implicitly set
    [#6021](#6021).
  * Improved error handling and type checking
    [#5981](#5981),
    [#5733](#5733),
    [#2904](#2904)
* OS X
  * MACOSX_DEPLOYMENT_TARGET has been bumped up to 10.7
    [#6402](#6402).
* Path
  * Improved type checking [#5348](#5348).
* Process
  * Introduce process warnings API
    [#4782](#4782).
  * Throw exception when non-function passed to nextTick
    [#3860](#3860).
* Readline
  * Emit key info unconditionally
    [#6024](#6024)
* REPL
  * Assignment to `_` will emit a warning.
    [#5535](#5535)
* Timers
  * Fail early when callback is not a function
    [#4362](#4362)
* TLS
  * Rename 'clientError' to 'tlsClientError'
    [#4557](#4557)
  * SHA1 used for sessionIdContext
    [#3866](#3866)
* TTY
  * Previously deprecated setRawMode wrapper is removed
    [#2528](#2528).
* Util
  * Changes to Error object formatting
    [#4582](#4582).
* Windows
  * Windows XP and Vista are no longer supported
    [#5167](#5167),
    [#5167](#5167).

jasnell added a commit that referenced this pull request

Apr 26, 2016 
The following significant (semver-major) changes have been made since the
previous Node v5.0.0 release.

* Buffer
  * New Buffer constructors have been added
    [#4682](#4682)
  * Previously deprecated Buffer APIs are removed
    [#5048](#5048),
    [#4594](#4594)
  * Improved error handling [#4514](#4514)
* Cluster
  * Worker emitted as first argument in 'message' event
    [#5361](#5361).
* Crypto
  * Improved error handling [#3100](#3100),
    [#5611](#5611)
  * Simplified Certificate class bindings
    [#5382](#5382)
  * Improved control over FIPS mode
    [#5181](#5181)
  * pbkdf2 digest overloading is deprecated
    [#4047](#4047)
* Dependencies
  * Reintroduce shared c-ares build support
    [#5775](#5775).
  * V8 updated to 5.0.71.31 [#6111](#6111).
* DNS
  * Add resolvePtr API to query plain DNS PTR records
    [#4921](#4921).
* Domains
  * Clear stack when no error handler
  [#4659](#4659).
* File System
  * The `fs.realpath()` and `fs.realpathSync()` methods have been updated
    to use a more efficient libuv implementation. This change includes the
    removal of the `cache` argument and the method can throw new errors
    [#3594](#3594)
  * FS apis can now accept and return paths as Buffers
    [#5616](#5616).
  * Error handling and type checking improvements
    [#5616](#5616),
    [#5590](#5590),
    [#4518](#4518),
    [#3917](#3917).
  * fs.read's string interface is deprecated
    [#4525](#4525)
* HTTP
  * 'clientError' can now be used to return custom errors from an
    HTTP server [#4557](#4557).
* Modules
  * Current directory is now prioritized for local lookups
    [#5689](#5689)
  * Symbolic links are preserved when requiring modules
    [#5950](#5950)
* Net
  * DNS hints no longer implicitly set
    [#6021](#6021).
  * Improved error handling and type checking
    [#5981](#5981),
    [#5733](#5733),
    [#2904](#2904)
* OS X
  * MACOSX_DEPLOYMENT_TARGET has been bumped up to 10.7
    [#6402](#6402).
* Path
  * Improved type checking [#5348](#5348).
* Process
  * Introduce process warnings API
    [#4782](#4782).
  * Throw exception when non-function passed to nextTick
    [#3860](#3860).
* Readline
  * Emit key info unconditionally
    [#6024](#6024)
* REPL
  * Assignment to `_` will emit a warning.
    [#5535](#5535)
* Timers
  * Fail early when callback is not a function
    [#4362](#4362)
* TLS
  * Rename 'clientError' to 'tlsClientError'
    [#4557](#4557)
  * SHA1 used for sessionIdContext
    [#3866](#3866)
* TTY
  * Previously deprecated setRawMode wrapper is removed
    [#2528](#2528).
* Util
  * Changes to Error object formatting
    [#4582](#4582).
* Windows
  * Windows XP and Vista are no longer supported
    [#5167](#5167),
    [#5167](#5167).